Process for the treatment of alloys



United States Patent The invention relates to the treatment of alloys used in storage battery plate grids, and more particularly to heat treatments with or without the application of additional physical treatment whereby the corrosion resistance and other characteristics of battery plates made from these alloys are substantially enhanced.

Battery plates made from lead-antimony alloys exhibit I notoriously poor resistance to corrosion by battery acid. It has therefore been proposed to use an alloy ha ing the following proportions:

Antimony 3-14 Arsenic 0.07 5-0.1 Copper 0.04-0.12 Lead Balance Such alloys have increased corrosion resistance and also have good mechanical strength.

It now has been found, however, that battery plate grids made from alloys of the above composition can even be more improved when, by a special treatment, the eutectie is changed after the casting process. it has been established that the especially high corrosion resistance of alloys as described above is discernible in their structure. If, for instance, a microsection of an ordinary binary antimony-lead alloy is compared with that of the above alloys, it becomes evident that a loosening of the eutectic has occurred. Since corrosion sets in primarily at the grain boundaries or at such points where the soft lead is separated by eutectic structures, corrosion decreases when fewer continuous eutectic particles are present in the section of the grid. If these eutectic particles are included, i.e., if they are interrupted by lead particles, it is to be assumed that the susceptibility of the alloy to corrosion likewise decreases.

According to the present invention, the loosening of the eutectic, visible in the structure of the cast, can be greatly improved by a strictly controlled heat treatment and, if desired, by additional deformation. Depending upon the antimony content of the alloy and upon the ensuing fabrication of the battery grid plates,- the process according to the invention can 'be applied in dilferent ways, as will be explained below. Often it is of advantage to subject the grid thus manufactured to an accelerated hardening process by quenching immediately after leaving the mold.

Different embodiments of the present invention now will be described. They all have in common the principle whereby the grid, after casting, is heat-treated for a period ranging from several hours to several days at 150 to 250 C. Afterward, the grid is allowed to cool slowly or more or less rapidly, depending upon manufacturing conditions. The manner of cooling does not afiect the increase in corrosion resistance since the latter is entirely independent therefrom. After the heat treatment, it can readily be recognized that the antimony phase of the eutectic has contraoted to spherical particles so that there isno longer a connection between the-several eutectic parts.

I The heating time can be shortened if,-before or during the heat treatment, the casting is subjected to strong deformation because internal stresses accelerate the process of inclusion and even permit the lowering of the temperature to less than 150 C. The deformation itself may be mechanical and can be effected by pressing, forging, stamping, rolling, etc. The stresses can also be produced by physical means, e.g., ultrasonically or by sudden temperature changes irom room temperature or elevated temperatures to very low temperatures. This yields the same effect as mechanical deformation.

If the temperature for the heat treatment is approximately in the middle of the limits named above (150- 250 C.), corrosion resistance will increase approximately 50 percent when the treatment is carried out for hours. This can be reduced to onethird the time if simultaneously a 60 percent deformation is effected. If the upper temperature limit is employed, only approximately 40 hours are required which can be shortened to 15 hours by application of a 60 percent deformation. When the temperatures are changed'rapi'dly between approximately 20 and -195 C., the same amount of time is required, i.e., approximately 40 hours, and also by application of ultrasonic waves. Naturally, the energy supplied ultrasonically or the cycles of temperature changes influence the inclusion, i.e., higher energy or more temperature changes permit shorter times to obtain the inclusion elfect.

In practice, several variations can be made according to the present invention. Grids made from alloys containing 3 to 6 percent antimony generally are of comparatively low strength which is evident particularly when the grid is to be used immediately after casting. It is opportune in such instances to subject the grid after casting and cooling in the mold, to quenching. This effects an instantaneous hardening, and the grid then withstands the mechanical deformation forces of the pasting process. Afterward, the grid filled with the mass is subjected to the bonding and drying process. This drying ordinarily is accomplished at temperatures up to 60 C. However, accordingto the present invention, drying is carried out at -250 so that in this manner the inclusion and, hence, the increased corrosion resistance is attained. The heat treatment has no detrimental efiect on the active mass. If the alloys contain more than 6 percent antimony, quenching is not required. Instead, the grids can be pasted immediately or, if desired, after hardening by storage, i.e., after 3-12 days. In this instance, also, drying can be accomplished after pasting and can be combined, as above, with the inclusion.

The heat treatment, of course, can also be cam'ed out on the grid before the active mass is applied thereto.

We claim as our invention:

1. A process for the manufacture of storage battery plates which comprises providing the plates with grids molded from alloys composed of 3-14 percent antimony, 0.075-0.1 percent arsenic, 0.04-0.12 percent copper, and the balance lead, heating said grids at 150-250 C. for 15 to 100 hours, and allowing them to cool slowly.

2. The process according to claim 1, wherein said grids are subjected to deformation prior to heating.

3. The process according to claim 1, wherein said grids are subjected to deformation during heating.

are quenched immediately after removal from the mold,

then are treated as defined in claim 1 and thereafter made into battery plates. 1, a j I t 7. The process according .to claim 1, wherein grids percent antimony are hardened by storing at room temperaturefor. 3 to 12 days, after removal from the mold, then are treated as defined in claim 1 and afiterward made into battery plates.

References Cited in the file of this patent UNITED STATES PATENTS 1,674,958 Dean et a1 June 26, 1928 1,675,644 Dean et a1 July 3, 1928 2,148,741 Gonser Feb. 28, 1939 OTHER REFERENCES Metals Handbook by the American Society f or Metals,

molded from alloys containing'morethan Sand upto 14 15 p. 1237,1948- V 

1. A PROCESS FOR THE MANUFACTURE OF STORAGE BATTERY PLATES WHICH COMPRISES PROVIDING THE PLATES WITH GRIDS MOLDED FROM ALLOYS COMPOSED OF 3-14 PERCENT ANTIMONY, 0.075-0.1 PERCENT ARSENIC, 0.04-0.12 PERCENT COPPER, AND THE BALANCE LEAD, HEATING SAID GRIDS AT 150-250*C. FOR 15 TO 100 HOURS, AND ALLOWING THEM TO COOL SLOWLY.
 2. THE PROCESS ACCORDING TO CLAIM 1, WHEREIN SAID GRIDS ARE SUBJECTED TO DEFORMATION PRIOR TO HEATING.
 3. THE PROCESS ACCORDING TO CLAIM 1, WHEREIN SAID GRIDS ARE SUBJECTED TO DEFORMATION DURING HEATING. 